An yttrium-based (RE-based) thin film wire known as a second-generation high-temperature superconducting wire has a thin tape shape with a thickness of about 0.1 mm.
When the wire is turned into a coil, what is generally used is the “pancake winding” by which the wire is wound spirally by bending the wire in a flatwise direction (or out-of-plane direction of the wire). In this case, from the wire that is wound around a reel, the tip of the wire is pulled out and fixed to a coil bobbin. Then, the coil bobbin is rotated so that the wire is wound around the coil bobbin. In this manner, a pancake-winding coil is produced.
The wire supply reel and the coil bobbin are placed on the same plane. Therefore, the coil can be wound without causing any distortion of the wire in an edgewise direction (or width direction of the wire).
For a magnet used in accelerators, what is required is a “saddle type coil” in which the wire is wound along the surface of a cylindrical beam duct. Unlike the pancake coil in which the wire is wound in a planar manner, the coil is produced as a three-dimensional winding having a steric shape.
In the case of a such coil, if the coil bobbin is rotated around one axis as in the case of the pancake winding, the position where the coil is wound would change in the width direction of the wire. If the positions of the wire reel and coil bobbin change in the width direction of the wire during the coil winding, stress is generated in such a way as to deform the wire in the edgewise direction.
The RE-based thin film wire includes a base plate made of nickel alloy, and is therefore high in rigidity. Accordingly, the wire does not easily deform in the edgewise direction, and kinks could emerge locally. Therefore, there is a risk of causing a deterioration of superconducting properties.
As disclosed in Patent Documents 1 and 2, what has been known is the techniques regarding the superconducting coil winding method for winding a tape-like superconducting wire without adding distortion as much as possible. However, while the techniques are effective in a double pancake winding or a layer winding, the techniques do not support three-dimensional windings such as the saddle type.